1. Field of the Invention
The present invention relates to a propolis extract with an improved water-solubility, more particularly, to a propolis extract wherein the water-solubility of the effective ingredients of propolis is improved by adjusting the pH of the propolis extract to 5.5-7.0, its preparation and uses, and to a method for improving the water-solubility of propolis extracts.
2. Description of the Prior Art
As is described in Propolis in Natural Therapeutics (1983), 2nd revised edition, published by Librairie Maloine S. A. Editeur, Paris, France, Fragrance Journal, No. 83, pp. 20-28 and pp. 36-43 (1987), and Apidologie, Vol. 22, pp. 155-162 (1991), propolis is a resin-like product, stored by bees in beehives, containing resins, beeswaxes, essential oils, pollens and flavonoids and having been used in a variety of folk medicines for a long time.
It has been known that the main activities of propolis are antiseptic activity, antioxidation activity, anti-inflammatory activity, local anesthesia, virus growth-inhibitory activity, immunoregulatory activity, and macrophage activating activity, and that the main ingredients of propolis are flavonoids, aromatic carboxylic acids, and aromatic aldehydes.
Prior to this invention, the present inventors had studied the effective ingredients of propolis. As a result, they found an effective ingredient, 3-4-hydroxy-3,5-bis(3-methyl-2-butenyl)phenyl!-2-propenoic acid, alias "Artepillin C" (hereinafter referred to as "substance C" throughout the specification), which exerts an antiseptic activity, hair growth activity, and antitumor activity, and established inventions relating to the uses of substance C: For example, Japanese Patent Laid-Open No. 256,177/94 discloses an antiseptic containing substance C as an effective ingredient, Japanese Patent Laid-Open No. 312,918/94 discloses a hair restorer containing substance C as an effective ingredient, and Japanese Patent Laid-Open No. 191,015/95 discloses an antitumor agent containing substance C as an effective ingredient.
As described above, the present inventors have already shown that substance C is one of the important ingredients in propolis.
Because propolis is a black and brown massive product and because it is mainly composed of water-insoluble hydrophobic products, it could not be readily used and is usually used in the form of a liquid propolis extract or of a propolis tincture by dissolving in and being extracted with high concentration solutions of readily water-soluble organic solvents, for example, acetone, acetic acid, and lower alcohols such as methanol, ethanol, isopropanol (or isopropyl alcohol). In general, ethanol is most favorably used.
Such a propolis extract, however, has a number of drawbacks when used in food products such as heath foods, agents of anti-susceptive diseases such as therapeutic and/or prophylactic agents for susceptive diseases, and cosmetics such as skin-refining agents and skin-whitening agents, and these drawbacks, listed below, render the applicability of propolis to a variety of fields difficult.
(1) The ingredients of the propolis extract such as resins and waxes are readily crystallized. When the propolis extract is diluted with saliva, the ingredients are readily crystallized, and this strongly inhibits their absorption and utilization by living bodies. When the propolis extract is diluted with water, the ingredients are crystallized in quantity, and this renders the handleability very difficult; PA1 (2) The color of the propolis extract is unsatisfactory and the extract easily changes to dark brown or opaque; and PA1 (3) The flavor and taste of the propolis extract are unsatisfactory, i.e. it has a muddy smell and a stimulant or sharp taste.
To overcome the drawbacks of conventional propolis extracts, the present inventors continued studying the concentration of readily water-soluble inorganic solvents.
As a result, the inventors established and disclosed in Japanese Patent Laid-Open No. 316,968/93 a purified propolis extract which has an absorbance ratio, A.sub.310 nm /A.sub.660 nm, of over 4,000 when the absorbances at 310 nm and 660 nm are converted into those at a concentration of 2 w/w % of the propolis extract, on a dry solid basis (throughout the specification, the wording "on a dry solid basis" is abbreviated as "d.s.b." and the above purified propolis extract may be referred to as "propolis extract), and established a propolis extract obtainable as a fraction by dissolving the effective ingredients of propolis in readily water-soluble inorganic solvents with a concentration of 30-55 v/v %.
During further study of propolis extracts, the present inventors found that when diluted with water according to conventional method, the propolis extracts partly came out of solution and became white suspensions containing insolubilized propolis ingredients. Detailed study revealed that most of the effective ingredients of propolis, especially, substance C, became insoluble.
Further study revealed that the effective ingredients of propolis readily dissolve in water-soluble inorganic solvents with a relatively high or middle concentration, but they are almost insoluble or substantially insoluble in the inorganic solvents when diluted with water, and this results in a serious drawback of hindering the exploitation of the valuable activities of the effective ingredients of propolis.